What is the recommended dosage of Mefenamic acid (nonsteroidal anti-inflammatory drug) for a female patient of reproductive age with dysmenorrhea and no significant medical history?

Dosage of Mefenamic Acid for Dysmenorrhea

For primary dysmenorrhea in reproductive-age women, administer mefenamic acid 500 mg as an initial loading dose, followed by 250 mg every 6 hours, starting at the onset of bleeding or pain (whichever comes first) and continuing for a maximum of 5-7 days during menstruation. 1

Specific Dosing Protocol

Initial Dose

• Loading dose: 500 mg (two 250 mg capsules) at symptom onset 1
• Begin treatment at the first sign of menstrual bleeding or pain, whichever occurs first 1

Maintenance Dosing

• 250 mg every 6 hours thereafter 1
• Continue for the duration of menstrual pain, typically 2-3 days 2
• Maximum treatment duration: 5-7 days per menstrual cycle 3, 1

Alternative Dosing Regimen

• Some protocols use 500 mg every 8 hours for up to 3 days, which has demonstrated 88.6% complete symptom relief 2, 4
• This higher-dose regimen may be considered for severe dysmenorrhea 4

Clinical Efficacy Evidence

The FDA-approved dosing regimen (500 mg loading dose, then 250 mg every 6 hours) was validated in controlled double-blind trials for primary spasmodic dysmenorrhea, demonstrating significant superiority over placebo across all pain parameters 1. The medication reduces menstrual blood loss by approximately 20% and decreases bleeding duration from a median of 7 days to 5 days 5.

Important Clinical Considerations

Duration Restrictions

• Mefenamic acid is FDA-approved only for short-term use (≤7 days) when treating dysmenorrhea 1
• Treatment should not exceed one week per menstrual cycle 1

Age Restrictions

• Only indicated for patients ≥14 years of age 1
• Has not been adequately studied in pediatric patients under 14 years 1

Administration Timing

• Take with food to minimize gastrointestinal side effects 3
• Starting treatment 1 day before expected menstruation may provide better symptom control 4

When This Regimen May Fail

Approximately 18% of women with dysmenorrhea do not respond adequately to NSAIDs including mefenamic acid 3. If symptoms persist after 2-3 treatment cycles:

• Consider hormonal contraceptives as second-line therapy (combined oral contraceptives with 30-35 μg ethinyl estradiol plus levonorgestrel or norgestimate) 3
• Evaluate for secondary causes: endometriosis, fibroids, polyps, adenomyosis, or pelvic inflammatory disease 3
• Extended or continuous cycle hormonal contraceptives are particularly effective for severe refractory dysmenorrhea 3

Contraindications and Precautions

Do not use mefenamic acid in patients with:

• Pre-existing renal disease or significantly impaired renal function 1
• Active peptic ulcer disease or gastrointestinal bleeding 1
• Known hypersensitivity to NSAIDs 1

Hepatic impairment requires dose reduction due to significant hepatic metabolism 1. The half-life in newborns is approximately five times longer than adults due to immature metabolic enzymes, underscoring the importance of the age restriction 1.

Adjunctive Non-Pharmacological Measures

While taking mefenamic acid, patients may benefit from:

• Heat therapy applied to the abdomen or lower back 3
• Acupressure at the LI4 point (dorsum of hand) and SP6 point (4 finger-widths above medial malleolus) 3
• Adequate rest and avoidance of overexertion during menstruation 3